Foamable phenolic resole resin compositions are known comprising a resole resin, a blowing agent and a surfactant. U.S. Pat. No. 3,389,094 discloses such systems. Such compositions have been optimized by the selection of the blowing agents and surfactants to improve foamability and the structure of the foams.
Such compositions are based on incompletely condensed phenolic resole resins of phenol and formaldehyde. When such compositions are mixed with an acid catalyst and a blowing agent, an exothermic reaction with further condensation causes liberation of gas by the blowing agent. The curing resin has an increased viscosity which prevents the escape of said gases and the composition expands to a foam with a substantially closed cell structure. Finally, the resin cures completely to a rigid foam of great utility for insulation uses. The cured phenol/aldehyde resole resins have fire and smoke retardant properties which can be increased further with certain additives giving added utility.
Acids are used to foam and cure such foams, hence, leave the cured foam with a pH below about 3 which is corrosive to metal building materials when the foams are used as building insulation. It is the objective of the present invention to provide foamable resole resin compositions that are curable to noncorrosive foams.